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Question: Are supplements which claim increased absorption or improved bioavailability telling the truth? Is it worth paying more for these? Are there concerns?
It is true that some supplements contain special ingredients, or enhancers, which can improve the absorption or bioavailability (amount of ingredient circulating in your blood) of certain supplements, such as CoQ10, curcumin, milk thistle, green tea, grape seed, ginkgo, and resveratrol. Enhancers typically act in the gut to either improve solubility or reduce the amount of enzymatic breakdown which occurs there. By allowing you to absorb more active ingredient, the supplement may be more potent, meaning that a smaller dose may be used. At the same time, enhancers may increase the absorption or otherwise interact with other supplements or drugs which you take, so it is important to use caution.
The four main types of enhancers currently found in supplements are emulsifying agents, like lecithin; self-emulsifying systems, which involve an oil; phytosomes made from phosphatidylcholine; and enzyme inhibitors, like black pepper extract. Liposomes and nanoparticles have also shown promise for improving absorption. Pros and cons of these enhancers, and the types of ingredients with which they may be useful, are discussed below (and in many of ConsumerLab.com's Product Reviews). See the full answer >> >>
Question: I take warfarin (Coumadin), an anticoagulant drug. Are there supplements I should avoid, or be taking, due to this drug?
Answer: Yes, the effectiveness of warfarin (Coumadin), anisindione (Miradon) and other anticoagulant drugs prescribed to help prevent blood clots can be impacted by taking supplements. This is discussed in detail in the Warfarin article, which is part of the extensive Drug Interactions section of our website (where you can look up interactions for other drugs you may be taking).
Examples of supplements which may increase warfarin’s blood-thinning effect (and, consequently, the risk of abnormal bleeding) are garlic, gingko and curcumin. Examples of supplements which may reduce warfarin’s ability to thin the blood include vitamin K, ginseng, St. John’s wort, and, in very high doses, green tea. CoQ10 is chemically similar to vitamin K2 and may also decrease the effects of warfarin, although the evidence for this is mixed. Because it can be affected by a large number of herbs, supplements and foods, it's important to consult your physician before taking any supplement with warfarin.
Question: I recently purchased some matcha green tea powder claiming to contain up to "137 times the EGCG" that is in brewed green tea. However, the label does not state an actual amount of EGCG and the company would not provide me with any analysis. Is the label true?
Answer: Although this “137 times” claim appears on a number of products, it appears to be false and based on misleading and borrowed science. This, and a concern with lead contamination in matcha, is explained in the “Brewed Green Tea vs. Matcha” section of the Green Tea Product Review >>
Question: Can L-theanine help as a sleep aid? Will ConsumerLab.com be testing these supplements?
Answer: L-theanine is an amino acid found in green and black tea. When given as a supplement in amounts higher than in a cup of tea, preliminary studies suggest a number of effects, such as improving mental alertness, reducing stress, and enhancing the quality of sleep -- although it does not cause drowsiness.
ConsumerLab.com has tested the quality of popular brands of L-theanine. You can find out how these L-theanine supplements fared in the tests; how they compare on quality and ingredients; which offer the best value; and learn about proper dosage and potential side effects in ConsumerLab.com's Review of L-Theanine Supplements >>
Question: Do any supplements help with gum disease or periodontitis?
Answer: Several different types of supplements may be helpful in improving gum disease and/or periodontitis -- the inflammation around the teeth causing pocketing -- such as DHA from algal oil, gamma-linolenic acid (GLA), lycopene, green tea, cranberry extract, and a certain type of probiotic. For details, including dosage, see the full answer >>
Question: Which supplements can help to lower blood pressure?
Answer: There are many supplements, including fish oil, curcumin, certain probiotics, cinnamon and others, which may lower blood pressure. However, if you already take medication to lower blood pressure, always consult your physician before using these supplements, as they may lower your blood pressure too much, or interfere in some other way with your current medication. Be aware that a number of supplements can increase blood pressure. Sign in to see the full answer >>
See the Encyclopedia article about Hypertension for more information.
Question: Which bottled green teas have the most EGCG?
In general, bottled green teas are a costly way to get EGCG, and some contain so little EGCG that you would have to drink an unrealistic amount in order to get the amount of EGCG found in brewable teas or supplements (which are, by far, the most cost effective way to get EGCG).
If you enjoy bottled tea, see our test results to see which contains the most EGCG — as well the amounts of caffeine we found in each, the sweeteners and calories they contain, and cost comparisons.
Question: After developing kidney stones, I was told to avoid tea -- but recently I've heard that green tea might actually be helpful for kidney stones. Is that true?
Answer: As discussed in the Green Tea Review, both black and green tea contain oxalate, high levels of which can contribute to the development of kidney stones in some people. However, for a number of reasons, this is not much of a concern with green tea (which may even help), and there are even ways to minimize the kidney-stone risk when drinking black tea. Get the details in the "Concerns and Cautions" section of the Green Tea Review >>
Be aware that too much calcium or vitamin C from supplements may increase the risk of kidney stones.
For information about other supplements that may be helpful or harmful regarding kidney stones, see the Encyclopedia article about Kidney Stones.
Question: How significant are the risks to drinking tea from China from heavy metals?
Answer: ConsumerLab.com and other research groups have found significant amounts of lead contaminating some teas from China. Contamination is most common in tea made from older leaves, as in black tea and Oolong tea, than from younger leaves used to make green tea. However, there are ways to reduce the health risks posed by contaminated products, as discussed in the "Lead" section of ConsumerLab.com's Green Tea Review >>. The Review includes test results and comparisons for teas sold loose, in tea bags, as matcha powder, and even as a K-Cup.
Question: What is Brain Bright and can it really improve memory or cognition?
Answer: Brain Bright (BioTrust Nutrition) is promoted on the company's website as a "science-backed" "triple-action brain enhancement formula" which promises to provide: 1) greatly improved memory and recall, 2) immediate concentration and razor-sharp focus and 3) second-to-none long-term brain health (by shielding the brain from toxins).
While the ingredients (and the amounts of these ingredients) in Brain Bright are each supported by some research suggesting a potential benefit, there are no published clinical studies on the effects of these ingredients when combined.
The claims made on the website appear to be based on an unpublished study, along with studies by others on the different ingredients listed in the product.
BioTrust provided ConsumerLab.com with a summary of the unpublished clinical trial -- which is cited on the company's website and referred to in this blog post by a BioTrust Nutrition "affiliate" (someone who is paid a commission for referring customers). The study involved 29 healthy adults between the ages of 19 and 68 (average age not given). It found that 2 tablets of Brain Bright taken daily for one week appeared to slightly reduce the number of mistakes on a test of concentration and short-term memory (approximately 1 mistake vs. 2.5 mistakes, respectively), but did not improve reaction time, processing speed or attention, compared to placebo. However, as data was not provided and the study results did not undergo peer-review for publication, it's difficult to draw any meaningful conclusions. In addition, no information about adverse effects was included.
Here is the evidence for each of the key ingredients in Brain Bright based on studies of the individual ingredients. You can use the links to get more information about each ingredient on ConsumerLab.com. Also shown is the amount of each ingredient listed in the suggested daily serving size of 2 tablets:
B Vitamins (riboflavin (8 mg), B-6 (20 mg), folate (as folic acid) (800 mcg), B-12 (methylcobalamin) (500 mcg) - The same doses of B-6, folic acid, and B-12, taken together, were found in one clinical study to slow cognitive decline in people age 70 years or older with mild cognitive impairment (riboflavin, however, was not used in the study).
Gingko biloba (240 mg of extract standardized to 24% glycosides, 6% lactones, and < 1 ppm ginkgolic acid) - Although this amount and type of extract is in-line with those used in some clinical studies for cognitive function, some experts have concluded there is little evidence that gingko improves cognitive function. The Brain Bright claim of "second-to-none long term brain health (by shielding the brain from toxins)" appears to be based on laboratory and animals studies demonstrating the antioxidant activity of ginkgo glycosides. However, we are not aware of any studies demonstrating long-term brain health benefits based on gingko's antioxidant properties.
Rhodiola rosea (200 mg root extract standardized to 5% rosavins and 2% salidrosides) — Doses in this range have shown some efficacy for improving certain measures memory and mental fatigue in a few small studies. However, overall, due to contradictory findings and design flaws in the studies, some researchers concluded there is insufficient evidence for this use.
N-acetyl-L-tyrosine (500 mg) - N-acetyl-L-tyrosine is converted into the amino acid tyrosine in the body. Although a few, small studies suggest tyrosine may improve memory or mental function in people who are sleep deprived or exposed to other forms of stress, it should be noted that these studies used higher doses of L-tyrosine (2,000 mg to 15,000 mg). In addition, it's not clear how much N-acetyl-L-tyrosine is actually converted into tyrosine in the body (Magnusson, Metabolism 1989; Van Goudoever, J Parenter Enteral Nutr 1994).
Acetyl-L-carnitine (500 mg) - There is some evidence that acetyl-L-carnitine may provide some help for age-related memory impairment, however, typically at a higher dosage (1,500 to 2,000 mg).
L-theanine (100 mg) - There is evidence that taking 50 mg of this amino acid (which is also found in black and green tea) may increase alpha brain wave activity, which plays an important role in attention, within less than an hour of taking. This research may be part of the basis for the claim that Brain Bright promise of "immediate concentration."
Brain Bright also contains 5 mg of black pepper extract (BioPerine), an ingredient which is sometimes added to supplements to enhance the bioavailability of certain ingredients.
It's important to note that the directions for use state: "Take 1 tablet 2 times daily, preferably without food, or, for enhanced concentration take 2 tablets as needed. Do not exceed 6 tablets per day." Taking the maximum recommended dosage of 6 tablets would provide three times the dosages of each ingredient as listed above. There are risks associated with taking such high doses of some of these ingredients, including vitamin B-6, B-12 and folic acid. Furthermore, there are no published studies on the safety of taking all of these ingredients together. For example, both Ginkgo biloba and Rhodiola may lower blood sugar, and both Rhodiola and L-theanine may lower blood pressure.
There are also potential interactions with medications for some of these ingredients. More information about potential side-effects and drug interactions for each ingredient can be found in the "Concerns and Cautions" sections of ConsumerLab.com's product reviews, which you can find by clicking on the above links to each review.
ConsumerLab.com has not tested Brain Bright to determine whether this product contains what it claims, and without contaminants.
Cost: Brain Bright costs $49 for a bottle containing 60 tablets - a 30 day supply if you take the recommended 2 per day. The website claims there is a one-year money back guarantee and you will not be enrolled in an auto-delivery program.
The bottom line:
Brain Bright contains several ingredients in doses which some small studies suggest may help to improve memory and cognition. However, there are no published clinical studies showing that these ingredients are safe or effective when taken together as in the Brain Bright formula. Furthermore, the overall evidence for two of its main ingredients, ginkgo and rhodiola, is currently considered insufficient for memory and cognition, and the evidence for the other ingredients is quite preliminary.
Question: Is it true that green tea can interact with blood-thinning medications like warfarin (Coumadin) or clopidogrel (Plavix)?
Answer: While green tea contains vitamin K and catechins — both of which have the potential to counteract the effects of some blood thinning medications -- drinking a moderate amount of regular brewed green tea would not be expected to cause a problem. (However, matcha green tea could potentially intefere with certain blood-thinning medications.) For more details about this and other potential drug and nutrient interactions of green tea, see the "Concerns and Cautions" section of the Green Tea Review >>
Question: How does white tea compare to green tea and black tea in terms of antioxidant catechins? How about caffeine levels and lead contamination?
Answer: White tea is made from the same leaves as green tea, but picked at a less mature stage. When brewed, white tea tends to provide comparable amounts of catechins (although, according to one study, much lower antioxidant activity overall), lower amounts of caffeine, and is less likely to be contaminated with lead than green tea. Bear in mind, however, that there can be considerable variation from product to product. For more details about how teas differ, see the "What to Consider When Buying" section of the Green Tea Review >>
Question: Can I take cholesterol-lowering statin medication with green tea?
Answer: Modest daily intake of green tea is not problematic for most people taking statins, but certain individuals may be more sensitive than others and certain statins may be more affected, as described in the Concerns and Cautions section of the Green Tea Review.
Green tea itself can help lower bad "LDL" cholesterol but, if you are on a statin, it may be best to limit green tea intake one cup per day, take your statin at a different time of day than green tea, and eliminate green tea altogether if you experience statin-related muscle pain.
For information about other potential interactions, see the Encyclopedia article about Statin Drugs article, which is part of the extensive Drug Interactions section of our website (where you can look up interaction for other drugs you may be taking).
Question: Are there vitamins or supplements that can reduce my risk of breast cancer?
Answer: There is not enough evidence to support the use of a particular vitamin or supplement to reduce the risk of breast cancer. However, associations have been found between intake of certain foods and food-based nutrients - such as omega-3 fatty acids, extra virgin olive oil, vitamin C and others - and reduced risk of breast cancer. Sign in to see the full answer >>
Question: Can green tea help prevent the flu?
Answer: Preliminary research suggests that drinking green tea during flu season may reduce the risk of getting the flu. Gargling with green tea may also help — a practice that is common in Japan. The evidence for green tea supplements, is less clear. More details are in the Flu section in the Green Tea Review. (which includes tests and comparisons of brewable green teas, supplements, matcha, and bottled green tea).
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Green Tea Review: Supplements, Brewable, Matcha, and Bottled
Initial Posting: 5/5/18 Last Update: 7/20/18
Find the Best Green Tea and Matcha, Including Supplements and Drinks
CL Tests Find Amounts of EGCG in Green Tea Products Vary Widely
Green tea supplements, brewable teas, matcha, and bottled drinks reviewed in report
Bigelow Green Tea - Decaffeinated
Kirkland (Costco) Green Tea A Blend of Sencha/Matcha
Salada Green Tea Naturally Decaffeinated
Celestial Seasonings Green Tea (K-Cup)
Kiss Me Organics Organic Matcha
Solgar Green Tea Leaf Extract
Davidson's Organics Gunpowder Green
Kroger Green Tea
Spring Valley [Walmart] Green Tea
GNC Herbal Plus Green Tea Complex
Life Extension Mega Green Tea Extract
Superfoods by MRM Raw Matcha Green Tea Powder
Green Foods Organic Matcha Green Tea
Lipton Green Tea
Swanson Superior Herbs Green Tea Extract
Harney & Sons Organic Green
NOW EGCg Green Tea Extract
Trader Joe's Specialty Teas Decaffeinated Green Tea
Numi Organic Tea Gunpowder Green
Twinings 100% Organic Pure Green
Honest Tea Green Tea with Honey
Organic Kenko Tea Matcha
Vitacost Green Tea Extract
Ito En Oi Ocha Unsweetened Green Tea
Organic Matcha DNA
Whole Foods Market Green Tea
Jade Leaf Organic Japanese Matcha
Pure Leaf Unsweetened Green Tea
Zhou Green Tea Extract
Make sure the green tea supplement, brewable tea, matcha, or drink you use passed our tests and is right for you!
Isn't your health worth it?
ConsumerLab.com tested the strength and purity of 30 green tea products to help you know what's really in them and how they compare.
Green tea contains EGCG and other polyphenol catechins that may reduce LDL cholesterol and lower the risk of developing cardiovascular disease, certain cancers and type 2 diabetes. However, amounts of these compounds in products vary enormously -- from as little as 20 mg to as much as 500 mg -- and are often incorrectly listed on labels or not listed at all.
Our tests also showed that when it comes to caffeine, you can't always trust what's listed on green tea product labels.
What's more, ConsumerLab found the cost to obtain an equivalent dose of EGCG to range from as little as 5 cents to more than $6.
You must be a ConsumerLab.com member to get the full green tea test results along with ConsumerLab's Top Picks and tips on how to choose and use green tea. You'll get results for 30 green tea products including supplements, brewable green teas, matcha powders, and bottled green tea beverages. Twenty-six of these were selected by ConsumerLab.com and four others passed the same testing in CL's voluntary Quality Certification Program. In the report, you'll learn:
ConsumerLab's Top Picks for green tea supplements, brewable teas, matcha powders and bottled green teas based on quality, value, and even taste
Which products passed or failed our tests and why
How much EGCG, total catechins, and caffeine is in each product
Why contamination with lead, cadmium and arsenic is a concern, and what our tests showed
Price comparisons showing how to get a green tea product with EGCG at the lowest cost
Clinical information about the efficacy of green tea and dosage
Cautions and potential side effects for green tea -- including drug interactions, a warning for women who are pregnant or nursing, liver toxicity, and effects on bones and teeth
Finding the Best Green Tea and Avoiding Dangers with CL Founder, Dr. Tod Cooperman
Learn More About Green Tea
ConsumerLab.com Answers -- for Green Tea Review: Supplements, Brewable, Matcha, and Bottled
Question: Are supplements which claim increased absorption or improved bioavailability telling the truth? Is it worth paying more for these? Are there concerns? Get the answer >>
Question: I take warfarin (Coumadin), an anticoagulant drug. Are there supplements I should avoid, or be taking, due to this drug? Get the answer >>
Question: I recently purchased some matcha green tea powder claiming to contain up to "137 times the EGCG" that is in brewed green tea. However, the label does not state an actual amount of EGCG and the company would not provide me with any analysis. Is the label true? Get the answer >>
Question: Can L-theanine help as a sleep aid? Will ConsumerLab.com be testing these supplements? Get the answer >>
Question: Do any supplements help with gum disease or periodontitis? Get the answer >>